Here and below by the expression “masterbatch mixing step” we mean a mixing step in which the polymer base is mixed with the other ingredients of the mix except for the vulcanization system.
Here and below by the expression “methylene donor chemical” we mean a chemical able to function as a cross-linking agent by means of methylene bridges in the presence of a “methylene acceptor” chemical.
On the market there is an increasing demand for tyres with low rolling resistance. In said regard, part of the research in the field of tyres is concentrated on finding solutions able to provide a low rolling resistance, without compromising the other tyre characteristics, for example the mechanical characteristics.
One of the possibilities of obtaining improvements in terms of rolling resistance is to reduce the quantity of reinforcing filler in the mix. However, reduction of the reinforcing filler normally results in a deterioration of the mechanical characteristics of the mix, such as the tensile strength, for example.
The need was therefore felt to improve the rolling resistance characteristics of a mix by reducing its quantity of reinforcing filler, without this entailing a deterioration of the mechanical characteristics of the mix.
For a more complete understanding of the present invention, it should be highlighted that long-term thermal and mechanical stability of the component rubber mixes is a particularly important characteristic for tyres.
It is known that the use of peroxide-based vulcanization systems or the so-called Efficient Vulcanization (EV) systems, characterised by a sulphur/accelerator ratio in favour of the latter, guarantees greater long-term thermal and mechanical stability to the detriment of process flexibility and fatigue resistance. Differently, the Conventional Vulcanization (CV) systems, characterised by a sulphur/accelerator ratio to the disadvantage of the latter, guarantee greater flexibility at the production stage and a greater fatigue resistance, but to the detriment of the long-term thermal and mechanical stability.
The Applicant has surprisingly devised a solution which allows a reduction in the quantity of reinforcing filler in the mix without deteriorating the mechanical characteristics and, at the same time, an improvement in the long-term stability characteristics of the mix.